Opto-Electronic Device With Two-Dimensional Injection Layers

ABSTRACT

An opto-electronic device with two-dimensional injection layers is described. The device can include a semiconductor structure with a semiconductor layer having one of an n-type semiconductor layer or a p-type semiconductor layer, and a light generating structure formed on the semiconductor layer. A set of tilted semiconductor heterostructures is formed over the semiconductor structure. Each tilted semiconductor heterostructure includes a core region, a set of shell regions adjoining a sidewall of the core region, and a pair of two-dimensional carrier accumulation (2DCA) layers. Each 2DCA layer is formed at a heterointerface between one of the sidewalls of the core region and one of the shell regions. The sidewalls of the core region, the shell regions, and the 2DCA layers each having a sloping surface, wherein each 2DCA layer forms an angle with a surface of the semiconductor structure.

REFERENCE TO RELATED APPLICATIONS

The present patent application claims the benefit of U.S. ProvisionalApplication No. 62/382,218, filed on 31 Aug. 2016, which is herebyincorporated by reference.

TECHNICAL FIELD

The present invention relates generally to opto-electronic devices suchas for example, ultraviolet light emitting diodes (UV LEDs), and moreparticularly, to devices that include tilted semiconductorheterostructures having two-dimensional carrier accumulation (2DCA)layers for improved carrier injection.

BACKGROUND ART

A great deal of interest has been focused on UV LEDs and lasers, inparticular those that emit light in the blue and deep ultraviolet (UV)wavelengths. These opto-electronic devices may be capable of beingincorporated into various applications, including solid-state lighting,biochemical detection, high-density data storage, and the like.

A modern opto-electronic device, such as a UV LED, typically includesthree major components: an electron supply layer (e.g., a n-typesemiconductor layer), a hole supply layer (e.g., a p-type semiconductorlayer), and a light generating structure formed between the electronsupply layer and the hole supply layer. These UV LEDs are mainlyfabricated from group III nitride heterostructures. Typically, a highlevel of p-type doping is necessary with the group III nitride materialsused in these heterostructures in order to have efficient LED operation.Achieving the necessary p-type doping for efficient operation is achallenge due to high ionization energy of acceptor impurities in thesegroup III nitride materials.

Several approaches have been used to attain the necessary p-type dopingin these group III nitride based UV LEDs. In one approach, an additionalSiO₂/semiconductor interface is used at the part of the UV LED where thehole accumulation layer is formed within a p-type layer. With thisapproach, the holes need to tunnel through the SiO₂/semiconductorinterface to reach the light generating structure. The hole accumulationlayer in this design can help increase the hole concentration, but theconcentration of holes tunneling through the SiO₂/semiconductorinterface is significantly lower than that in the hole accumulationlayer. Also, adding the SiO₂/semiconductor interface in this designsubstantially increases the turn-on voltage of the UV LED device.

In another approach, a tunnel junction formed between two group IIInitride layers is used for hole injection into the light generatingstructure. In this approach, a high electron concentration in the topgroup III nitride layer causes carrier tunneling through the tunneljunction and reduces the lateral spreading resistance. However, thisdesign does not allow for significant improvement in the hole injectioninto the light generating structure. In a third approach, a holeacceleration layer is used with the UV LED device structure. Inparticular, a group III nitride layer and a group III nitride barrierform a region with strong electric field enhancing the hole emissionover the barrier. This approach results in excessive voltage drop acrossthe additional barrier without any significant increase in the holeinjection into the light generating structure. All of these designapproaches for group III nitride based UV LEDs lack the capability toenable high carrier concentration in the light generating structure dueto high ionization energy of the doped group III nitride materials.

SUMMARY OF THE INVENTION

This summary of the invention introduces a selection of certain conceptsin a brief form that are further described below in the detaileddescription of the invention. It is not intended to exclusively identifykey features or essential features of the claimed subject matter setforth in the claims, nor is it intended as an aid in determining thescope of the claimed subject matter.

Aspects of the present invention are directed to improving carrierinjection in opto-electronic devices such as for example, UV LEDs.Improved carrier injection is obtained in the various embodiments of thepresent invention by forming two-dimensional gas (2DG) layers at ahetero-interface between two materials with different compositions inorder to enhance hole/electron injection efficiency.

In one embodiment, a set of tilted semiconductor heterostructures isformed over a semiconductor structure which can include an n-typesemiconductor layer or a p-type semiconductor layer, and a lightgenerating structure formed on the semiconductor structure. Each tiltedsemiconductor heterostructure can include a core region and a set ofshell regions each adjoining a sidewall of the core region. The tiltedsemiconductor heterostructure also include a set of two-dimensionalcarrier accumulation (2DCA) layers, with each 2DCA layer formed at aheterointerface between one of the sidewalls of the core region and oneof the shell regions.

The core region and the shell regions of each of the tiltedsemiconductor heterostructures can include a combination of differentmaterials selected from group III-V elements. In one embodiment, thecore region and shell regions can include group III nitride elementssuch that a concentration of at least one of the group III nitrideelements in the core region is different from a concentration of thatgroup III nitride element in the pair of shell regions. In one example,the group III nitride elements in the core region and shell regions caninclude a material represented by the Al_(x)Ga_(1-x)N system, whereinthe pair of shell regions have different compositions of Al than thecomposition of Al in the core region. In one embodiment, the core regioncan contain a higher concentration of Al than the concentration of Al inthe pair of shell regions. In one embodiment, the pair of shell regionscan have a different composition of AIN than the composition of AlN inthe core region, wherein the core region contains a higher concentrationof AlN than the concentration of AlN in the pair of shell regions.

The combination of different materials in each of the tiltedsemiconductor heterostructures, between the core region and the shellregions, form a 2DG layer at an interface between the combination ofdifferent materials. In particular, a 2DG is formed in each of the 2DCAlayers separating a side of the core region with one of the shellregions. Depending on the semiconductor structure, the 2DG layer caninclude either a two-dimensional hole gas (2DHG) or a two-dimensionalelectron gas (2DEG). For example, if the semiconductor structureincludes an electron blocking layer, then 2DHGs can be formed in the2DCA layers between the core region and the shell regions.Alternatively, if the semiconductor structure includes a hole blockinglayer, then 2DEGs can be formed in the 2DCA layers between the coreregion and the shell regions.

In each tilted semiconductor heterostructure, the sidewalls of the coreregion, the pair of shell regions, and the pair of 2DCA layers have asloping surface, such that each 2DCA layer forms an angle with a surfaceof the semiconductor structure. The efficient injection of holes fromthe 2DCA layers to the light generating structure in the semiconductorstructure is a function of the angle formed between each of the 2DCAlayers and the surface of the semiconductor structure. In oneembodiment, an angle that ranges from 30 degrees to 60 degrees has beendetermined to provide efficient carrier injection.

The tilted semiconductor heterostructures can be formed from anassortment of shapes and sizes (e.g., height, thickness, etc.) havingtilted surfaces. In one embodiment, the tilted semiconductorheterostructures have a conical shape. Other shapes can include, but arenot limited to, structures having inclined shapes, e.g., at least oneinclined side, such as a trapezoid. In one embodiment, the tiltedsemiconductor heterostructures formed over the semiconductor structurecan include heterostructures with different shapes and sizes.

A supply electrode can be formed over the tilted semiconductorheterostructures. In one embodiment, the pairs of the 2DCA layers ineach of the tilted semiconductor heterostructures can contact the lightgenerating structure of the semiconductor structure and the supplyelectrode to form injection zones for charge carriers. In this manner, asource applied to the supply electrode can drive holes/electrons fromthe heterostructures into the light generating structure in thesemiconductor structure for electron-hole pair recombination and lightemission therefrom. Depending on the polarity of the tiltedsemiconductor heterostructures, the supply electrode can form an anodeor a cathode to the device. For example, if the tilted semiconductorheterostructures are p-type, then the supply electrode can form ananode. Alternatively, if the tilted semiconductor heterostructures aren-type, then the supply electrode can form a cathode. In one embodiment,one or both electrodes (one formed at the top of the device and one atthe bottom) which can form the anode and cathode can include transparentcontacts.

In one embodiment, a doped semiconductor layer can be formed between thetilted semiconductor heterostructures and the supply electrode. To thisextent, the doped semiconductor layer and the tilted semiconductorheterostructure can form a multi-layered structure. This dopedsemiconductor layer facilitates the electric contact between the supplyelectrode and the 2DCA layers in each of the tilted semiconductorheterostructures by reducing the total resistance of the device. In oneembodiment, the doped semiconductor layer can include discontinuoussections of the doped semiconductor layer. In this manner, eachdiscontinuous section of the doped semiconductor layer can be formed onone of the tilted semiconductor heterostructures.

Each of the tilted semiconductor heterostructures can be separated fromimmediately adjacent heterostructures by a predetermined spacing. Theamount of spacing between each of the tilted semiconductorheterostructures can vary depending on the application of the device.For example, in sensing applications, the spacing between the tiltedsemiconductor heterostructures can be increased to permit gases and/orliquids to travel therethrough and contact the surface of thesemiconductor structure. The spacing between the tilted semiconductorheterostructures can also have a role in enabling the device to achievea targeted total output of optical power. For example, in a scenariowhere the tilted semiconductor heterostructures are used to form anopto-electronic device having an array of UV LEDs, the device cangenerate a higher total output of optical power if the spacing betweenheterostructures is smaller because more heterostructures can beconfigured in the array.

In one embodiment, the shell regions of each tilted semiconductorheterostructure can include a plurality of compositional layers formedon the sidewalls of the core region that extend laterally away from thecore region. Each compositional layer can have a different compositionfrom an immediately adjacent compositional layer. In this manner, a 2DGlayer can be formed between each of the compositional layers. Thecompositional layers can include group III-V materials. In oneembodiment, the group III-V material can include a material representedby the Al_(x)Ga_(1-x)N system. In one embodiment, each of the layers caninclude a different composition of Al. In another embodiment, each ofthe layers can include a different composition of AlN.

A core region of the tilted semiconductor heterostructures that issurrounded by compositional layers can include a multilayered structureof horizontally extending layers. In one embodiment, the multilayeredstructure can include a short period superlattice (SPSL) having a set ofbarriers alternating with a set of quantum wells. The SPSL can betransparent to a targeted radiation at a normal incidence to the SPSL.In one embodiment, the barriers and the quantum wells of the SPSL caninclude alternating Al_(x)Ga_(1-x)N/Al_(y)Ga_(1-y)N pairs, with eachlayer within a pair including a thin semiconductor layer having athickness ranging from 0.5 nm to 20 nm.

In one embodiment, ohmic contacts can be formed over the tiltedsemiconductor heterostructures. For example, each ohmic contact can beformed on one of the tilted semiconductor heterostructures, such thatthe ohmic contact extends along a top surface of the core region and theset of shell regions and down a side portion of each shell region.

In one embodiment, a dielectric layer can be formed in the spacesbetween each of the tilted semiconductor heterostructures forpassivation. The dielectric layer can be transparent to a targetedradiation at a normal incidence to the dielectric layer. A reflectivemetallic contact can also be formed over the ohmic contacts and thedielectric layer. The reflective properties of the reflective metalliccontact can be improved by depositing Bragg mirrors between the tiltedsemiconductor heterostructures before forming the metallic contact.Another embodiment can include adding light scattering elements in thedielectric layer that scatter light that is at least 10% Lambertian. Inone embodiment, another SPSL having a set of barriers alternating with aset of quantum wells, and a graded semiconductor layer can be formedbetween the tilted semiconductor heterostructures and the semiconductorstructure.

The compositional layers that surround the sides of the core region oftilted semiconductor heterostructures can include a graded compositionof material. This graded composition, in addition to the formation ofthe 2DG at the interface of the layers can result in polarization dopingof the tilted semiconductor heterostructures that can include eitherp-type doping or n-type doping. The graded composition provides controlof the spreading of the 2DG within the compositional layers. The gradedcomposition of material can vary in the compositional layer in avertical direction, a lateral direction or a combination of both thevertical direction and the lateral direction.

Besides controlling electrical properties, the materials of thecompositional layers as well as the thicknesses of the layers can beselected to control the optical properties of the tilted semiconductorheterostructures. For example, in one embodiment, the compositionallayers in the tilted semiconductor heterostructures can form Braggreflectors. In another embodiment, the compositional layers in thetilted semiconductor heterostructures can form graded refractive indexstructures to improve light extraction. In these embodiments, the coreregion of each tilted semiconductor heterostructure can be transparentto a targeted radiation at a normal incidence to the core region.

In one embodiment, the tilted semiconductor heterostructures can includea tilted nanowire. In this implementation, each tilted nanowire caninclude a core region and shell regions surrounding the sides of thecore region, with a 2DCA layer formed between the interface of the coreregion and each shell region. The core region and the shell regions canhave different compositions of materials, which form the 2DGs in each ofthe 2DCA layers at the interface between the different materials. Eachof the nanowires can be epitaxially grown under an angle with respect toa surface of the light generating structure of the semiconductorstructure. In this manner, direct contact between the 2DHGs and thesupply electrode as well as between the 2DHGs and the light generatingstructure can be attained to facilitate efficient carrier injection. Anangle that ranges from 30 degrees to 60 degrees will provide efficientcarrier injection for these nanowires.

A first aspect of the invention provides a device, comprising: asemiconductor structure having a semiconductor layer including one of ann-type semiconductor layer or a p-type semiconductor layer, and a lightgenerating structure formed on the semiconductor layer; and a pluralityof tilted semiconductor heterostructures formed over the semiconductorstructure, each tilted semiconductor heterostructure separated from anadjacent tilted semiconductor heterostructure by a predeterminedspacing, each tilted semiconductor heterostructure including a coreregion, a set of shell regions, each shell region adjoining a sidewallof the core region, and a set of two-dimensional carrier accumulation(2DCA) layers, each 2DCA layer formed at a heterointerface between oneof the sidewalls of the core region and one of the shell regions, thesidewalls of the core region, the set of shell regions and the set of2DCA layers each having a sloping surface, wherein each 2DCA layer formsan angle with a surface of the semiconductor structure, the angleranging from 30 degrees to 60 degrees.

A second aspect of the invention provides a device, comprising: asubstrate; an n-type semiconductor layer formed over the substrate; alight generating structure formed on the n-type semiconductor layer; aplurality of spaced conically-shaped p-type heterostructures formed overthe light generating structure, each conically-shaped p-typeheterostructure including a core region and a set of shell regions eachadjoining a sidewall of the core region, wherein a two-dimensional holegas (2DHG) layer is formed at a heterointerface between each of thesidewalls of the core region and the shell regions, the sidewalls of thecore region, the set of shell regions, and the 2DHG layers each having atilted surface that slopes increasingly inward from a bottom surface ofthe core region, the pair of shell regions, and the 2DHGs to a topsurface thereof, wherein the heterointerface forms an angle with asurface of the light generating structure, the angle ranging from 30degrees to 60 degrees; and a supply electrode formed over the pluralityof conically-shaped p-type heterostructures.

A third aspect of the invention provides an opto-electronic device,comprising: an ultraviolet transparent substrate; an n-typesemiconductor layer formed over the ultraviolet transparent substrate,the n-type semiconductor layer having an Al_(x)Ga_(1-x)N composition; alight generating structure formed on the n-type semiconductor layer, thelight generating structure including a plurality of barriers alternatingwith a plurality of quantum wells, the plurality of barriers and theplurality of quantum wells having an Al_(x)Ga_(1-x)N composition,respectively, with x<y; a p-type semiconductor structure formed over thelight generating structure, the p-type semiconductor structure includingat least one layer including a set of tilted semiconductorheterostructures, each tilted semiconductor heterostructure separatedfrom an adjacent tilted semiconductor heterostructure by a predeterminedspacing and having a lateral area that is no larger than 20% of alateral area of the light generating structure, each tiltedsemiconductor heterostructure having an Al_(x)Ga_(1-x)N composition,each tilted semiconductor heterostructure including a core region and aset of shell regions, each shell region adjoining a sidewall of the coreregion, wherein the core region includes a first AlN molar ratio andeach of the shell regions surrounding the core region include a secondAlN molar ratio, the first AIN molar ratio being greater than the secondAlN molar ratio.

The illustrative aspects of the invention are designed to solve one ormore of the problems herein described and/or one or more other problemsnot discussed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of the disclosure will be more readilyunderstood from the following detailed description of the variousaspects of the present invention taken in conjunction with theaccompanying drawings that depict various aspects of the invention.

FIG. 1 shows a cross-sectional view of an opto-electronic device havinga set of tilted semiconductor heterostructures formed over asemiconductor structure having a light generating structure and ann-type semiconductor layer, in which each heterostructure includes 2DGlayers at a heterointerface between two materials with differentcompositions according to an embodiment.

FIG. 2 shows a more detailed cross-sectional view of one of the tiltedsemiconductor heterostructures depicted in FIG. 1 along with aqualitative band diagram showing the formation of one of the 2DG layersat the heterointerface between the two materials with differentcompositions according to an embodiment.

FIG. 3 shows another detailed cross-sectional view of one of the tiltedsemiconductor heterostructures with an angle formed between one of the2DG layers and a bottom surface of the heterostructure according to anembodiment.

FIG. 4 illustrates the relationship between the angle depicted in FIG. 3and the amount of polarization charge that is induced at theheterointerface between the two materials with different compositionsaccording to an embodiment.

FIG. 5 shows a cross-sectional view of an opto-electronic device havinga doped semiconductor layer formed between the set of tiltedsemiconductor heterostructures and a supply electrode according to anembodiment.

FIG. 6 shows the opto-electronic device of FIG. 1 having increasedspacing between each of the tilted semiconductor heterostructures foruse in sensing applications in which gases and/or liquids are permittedto travel therethrough and contact the surface of the semiconductorstructure according to an embodiment.

FIG. 7 shows a cross-sectional view of an opto-electronic device havinga set of tilted semiconductor heterostructures formed over asemiconductor structure having a light generating structure and a p-typesemiconductor layer, in which each heterostructure includes 2DG layersat a heterointerface between two materials with different compositionsaccording to an embodiment.

FIG. 8 shows a schematic of an opto-electronic device forming an arrayof pixels in which the pixels take the form of the tilted semiconductorheterostructures described herein according to an embodiment.

FIG. 9 shows a cross-sectional view of an opto-electronic device havinga set of tilted semiconductor heterostructures in which eachheterostructure includes a core region with a set of shell regionsadjoining the sidewalls of the core region, wherein the shell regionsinclude a set of compositional layers according to an embodiment.

FIG. 10 shows a cross-sectional view of an opto-electronic device havinga set of tilted semiconductor heterostructures in which eachheterostructure includes a core region with a set of shell regionsadjoining the sidewalls of the core region, wherein the core regionincludes a multilayered structure and the shell regions include a set ofcompositional layers according to an embodiment.

FIG. 11 shows an alternative to the opto-electronic device of FIG. 10 inwhich a set of ohmic contacts is formed over the tilted semiconductorheterostructures, a dielectric layer is formed in between theheterostructures, and a reflective metallic contact is formed over theohmic contacts and the dielectric layer according to an embodiment.

FIG. 12 shows an alternative to the opto-electronic device of FIG. 11 inwhich light scattering elements are formed in the dielectric layeraccording to an embodiment.

FIG. 13 shows another detailed cross-sectional view of one of the tiltedsemiconductor heterostructures in which the compositional layers of theshell region have graded compositions of material that vary in avertical direction according to an embodiment.

FIG. 14 shows another detailed cross-sectional view of one of the tiltedsemiconductor heterostructures in which the compositional layers of theshell region have graded compositions of material that vary in a lateraldirection according to an embodiment.

FIGS. 15A-15B show the effect that a heterostructure with and without agraded composition of material has on the spreading of a 2DG layer asrepresented by the carrier density profiles in the figures according toan embodiment.

FIG. 16 shows another detailed cross-sectional view of one of the tiltedsemiconductor heterostructures in which the core region is transparentand the compositional layers of the shell region form a Bragg reflectorstructure according to an embodiment.

FIG. 17 shows another detailed cross-sectional view of one of the tiltedsemiconductor heterostructures in which the core region includes aplurality of core regions adjoined by shell regions having a pluralityof compositional layers according to an embodiment.

FIG. 18 shows a cross-sectional view of an opto-electronic device havinga plurality of tilted semiconductor heterostructures formed from aplurality of nanowires in which each nanowire includes 2DG layers at aheterointerface between two materials with different compositionsaccording to an embodiment.

FIG. 19 shows an illustrative flow diagram for fabricatingopto-electronic devices having a set of tilted semiconductorheterostructures according to one of the various embodiments describedherein.

It is noted that the drawings may not be to scale. The drawings areintended to depict only typical aspects of the invention, and thereforeshould not be considered as limiting the scope of the invention. In thedrawings, like numbering represents like elements between the drawings.

DETAILED DESCRIPTION OF THE INVENTION

The various embodiments are directed to improving carrier injection inopto-electronic devices such as UV LEDs. Improved carrier injection isobtained in the various embodiments of the present invention by forming2DG layers at a heterointerface between two materials with differentcompositions. In one embodiment, a set of tilted semiconductorheterostructures can be formed over a single or multi-layeredsemiconductor structure having a light generating structure. Each of thetilted semiconductor heterostructures can include a core region and aset of shell regions that each adjoin a sidewall of the core region. Thecore region and the set of shell regions can include differentcompositions of the same material. The heterointerface between the coreregion and the shell regions leads to the formation of 2DG layers at theinterface between the two materials with different compositions.

As used herein, an opto-electronic device can include any light emittingdevice or solid state lighting source (SSLS) that uses one or more ofany diode that under normal operating conditions can generate radiation.More specifically, the opto-electronic device can include any lightemitting device or SSLS that uses semiconductor LEDs. Examples ofsemiconductor LEDs can include, but are not limited to, UV LEDs,conventional and super luminescent LEDs, light emitting solid statelasers, laser diodes of various types, and/or the like. These examplesof semiconductor LEDs can be configured to emit electromagneticradiation from a light generating structure such as an active regionupon application of a bias. The electromagnetic radiation emitted bythese semiconductor LEDs can comprise a peak wavelength within any rangeof wavelengths, including visible light, ultraviolet radiation, deepultraviolet radiation, infrared light, and/or the like. For example,these semiconductor LEDs can emit radiation having a dominant wavelengthwithin the ultraviolet range of wavelengths. As an illustration, thedominant wavelength can be within a range of wavelengths ofapproximately 210 nanometers (nm) to approximately 350 nm.

Any of the various layers that form the opto-electronic device can beconsidered to be transparent to radiation of a particular wavelengthwhen the layer allows an amount of the radiation radiated at a normalincidence to an interface of the layer to pass there through. Forexample, a layer can be configured to be transparent to a range ofradiation wavelengths corresponding to a peak emission wavelength forlight, such as ultraviolet light or deep ultraviolet light, emitted bythe active region of the opto-electronic device (e.g., peak emissionwavelength +/−five nanometers). As used herein, a layer is transparentto radiation if it allows more than approximately five percent of theradiation to pass there through, while a layer can also be considered tobe transparent to radiation if it allows more than approximately tenpercent of the radiation to pass there through in a more particularembodiment. Defining a layer to be transparent to radiation in thismanner is intended to cover layers that are considered transparent andsemi-transparent.

A layer of the opto-electronic device can be considered to be reflectivewhen the layer reflects at least a portion of the relevantelectromagnetic radiation (e.g., light having wavelengths close to thepeak emission of the light generating structure). As used herein, alayer is partially reflective to radiation if it can reflect at leastapproximately five percent of the radiation, while a layer can also beconsidered to be partially reflective if it reflects at least thirtypercent for radiation of the particular wavelength radiated normally tothe surface of the layer. A layer can be considered highly reflective toradiation if it reflects at least seventy percent for radiation of theparticular wavelength radiated normally to the surface of the layer.

The description that follows may use other terminology herein for thepurpose of describing particular embodiments only and is not intended tobe limiting of the disclosure. For example, unless otherwise noted, theterm “set” means one or more (i.e., at least one) and the phrase “anysolution” means any now known or later developed solution. The singularforms “a,” “an,” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise. It will be furtherunderstood that the terms “comprises”, “comprising”, “includes”,“including”, “has”, “have”, and “having” when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Turning to the drawings, FIG. 1 shows a cross-sectional view of anopto-electronic device 10 having a set of tilted semiconductorheterostructures 12 formed over a semiconductor structure 14 having alight generating structure 16 and an n-type semiconductor layer 18, inwhich each heterostructure 12 includes 2DG layers 20A, 20B at eachheterointerface 22 between two materials with different compositionsaccording to an embodiment. As used herein, a tilted semiconductorheterostructure means a heterostructure having at least oneheterointerface that is positioned such that the normal direction drawnto the heterointerface is not parallel to the growth direction. FIG. 1shows that the set of tilted semiconductor heterostructures 12 can beformed between the light generating structure 16 and a supply electrode24, while the n-type semiconductor layer 18 of the semiconductorstructure 14 can be formed on a substrate/buffer 26. In one embodiment,the set of tilted semiconductor heterostructures 12 can comprise aplurality of domains each domain having lateral area that is smallerthan a lateral area of the light generating structure 16. In a moreparticular embodiment, each domain has a maximum lateral area that is nolarger than 20% of a lateral area of the light generating structure 16.

Each tilted semiconductor heterostructure 12 can be separated from anadjacent tilted semiconductor heterostructure by a predetermined spacingS (as measured at the base of each heterostructure 12). In anembodiment, the spacing between the heterostructures 12 is filled with adielectric, such as ambient air. Furthermore, each tilted semiconductorheterostructure 12 can include a core region 28, a set of shell regions30 (shown as a pair of opposing shell regions 30), with each shellregion adjoining a sidewall of the core region. In one embodiment, eachshell region 30 laterally surrounds the core region 28 at least over 10%of the core region lateral boundary. In an embodiment, the shell regions30 are part of a single shell region that completely surrounds a lateralarea of the core region 28. A pair of two-dimensional carrieraccumulation (2DCA) layers are formed at each heterointerface 22 thatincludes a 2DG layer 20A, 20B. In particular, each 2DCA layer is formedbetween one of the sidewalls of the core region 28 and one of the shellregions 30.

As shown in FIG. 1, the sidewalls of the core region 28, the pair ofshell regions 30 and the pair of 2DCA layers at the heterointerface 22each have a sloping surface. Each 2DCA layer at the heterointerface 22forms an angle θ with a surface of the semiconductor structure 14 (e.g.,the light generating structure 16). In one embodiment, the angle θ canrange from 30 degrees to 60 degrees. As illustrated, the angle θ can bemeasured in any polar direction. While the angle 8 is shown as being thesame for each tilted semiconductor heterostructure 12, it is understoodthat the angles θ can vary for different polar directions of aheterostructure 12 and/or between the different heterostructures 12.

The tilted semiconductor heterostructures can be formed from anycombination of one or more of an assortment of shapes and sizes (e.g.,height, thickness, etc.) having tilted surfaces. In one embodiment, asshown in FIG. 1, the tilted semiconductor heterostructures 12 can have aconical shape. Other shapes can include, but are not limited to,pyramids of various cross-sectional shapes.

The substrate/buffer 26 is illustrated in FIG. 1 as one element,however, it is understood that the substrate and buffer can compriseseparate elements. In one embodiment, the set of tilted semiconductorheterostructure 12 and the semiconductor structure 14 including thelight generating structure 16 and the n-type semiconductor layer 18 canbe formed on a buffer layer, which can be formed on the substrate. Inother embodiments, it is understood that the opto-electronic device 10may not include a substrate/buffer 26.

In one embodiment, the substrate can include sapphire, silicon carbide(SiC), silicon (Si), GaN, GaAs, AlGaN, AlON, LiGaO₂, InP, AlN, AIII-BVor AIIBVI compounds, SiO₂, Si₃N₄, diamond or other suitable material,and the buffer layer can include AlN, an AlGaN/AlN superlattice, and/orthe like. In one embodiment, the substrate can include a non-conductiveor insulating substrate. Examples of a non-conductive or insulatingsubstrate can include highly-resistive silicon, insulating SiC,sapphire, diamond, a dielectric material, organic materials, and/or thelike.

The semiconductor structure 14 can include a single or multi-layeredstructure having the light generating structure 16. In the embodimentdepicted in FIG. 1, the semiconductor structure 14 is a multi-layerstructure including the light generating structure 16 and the n-typesemiconductor layer 18. The light generating structure 16 can form theactive region of the opto-electronic device 10. In one embodiment, thelight generating structure can include a multi-quantum well structurehaving a set of barrier layers alternating with a set of well layers. Inthe embodiment depicted in FIG. 1, the n-type semiconductor layer 18 canform an electron supply layer, while the set of tilted semiconductorheterostructures 12 can form a hole supply layer. In this manner, thelight generating structure 16, the n-type semiconductor layer 18, andthe set of tilted semiconductor heterostructures 12 form aheterostructure within the opto-electronic device 10 that serves as theactive p-n junction region for electron-hole pair recombination andlight emission.

The supply electrode 24, which can be a metal electrode, acts as theanode side of the opto-electronic device 10. In one embodiment, thesupply electrode 24 can form a transparent contact to the set of tiltedsemiconductor heterostructures 12 which is generally a p-typesemiconductor structure. A source (not shown) applied to the supplyelectrode 24 can drive electrons from the n-type semiconductor layer 18to the light generating structure 16 and holes in the 2DCA layers at theheterointerfaces 22 of the tilted semiconductor heterostructures 12 tothe light generating structure 16 for electron-hole pair recombinationand light emission therefrom.

The light generating structure 16, the n-type semiconductor layer 18 andthe set of tilted semiconductor heterostructures 12 of theelectro-optical device 10 can form a group III-V materials based-device,in which some or all of the various layers are formed of elementsselected from the group III-V materials system that can be grown on thesubstrate/buffer 26 by epitaxial or other methods. In a more particularillustrative embodiment, the various layers of the light generatingstructure 16, the n-type semiconductor layer 18 and the set of tiltedsemiconductor heterostructures 12 can be formed of group III nitridebased materials. Group III nitride materials comprise one or more groupIII elements (e.g., boron (B), aluminum (Al), gallium (Ga), and indium(In)) and nitrogen (N), such that B_(W)Al_(X)Ga_(Y)In_(Z)N, where 0≦W,X, Y, Z≦1, and W+X+Y+Z=1. Illustrative group III nitride materials caninclude binary, ternary and quaternary alloys such as, AlN, GaN, InN,GaAs, GaInAs, GaInP, BN, AlGaN, AlInGaN, AlInN, AlBN, AlGaInN, AlGaBN,AlInBN, and AlGaInBN with any molar fraction of group III elements. Itis understood that this other group III nitride materials are fullyapplicable and that this illustrative list is not meant to limit thescope of the various embodiments.

An illustrative embodiment of a group III nitride based light generatingstructure 18 that includes a multi-quantum well (e.g., a series ofalternating quantum wells and barriers) can compriseIn_(y)Al_(x)Ga_(1-x-y)N, Ga_(z)In_(y)Al_(x)B_(1-x-y-z)N, anAl_(x)Ga_(1-x)N semiconductor alloy, or the like. In one embodiment, thelight generating structure 16 can include a set of quantum wells andbarriers having an Al_(x)Ga_(1-x)N and an Al_(y)Ga_(1-y)N compositionrespectively, with x<y.

Similarly, both the n-type semiconductor layer 18 and the set of tiltedsemiconductor heterostructures 12 and can be composed of anIn_(y)Al_(x)Ga_(1-x-y)N alloy, a Ga_(z)In_(y)Al_(x)B_(1-x-y-z)N alloy,or the like. The molar fractions given by x, y, and z can vary betweenthe various layers of the light generating structure 16, the n-typesemiconductor layer 18, and the set of tilted semiconductorheterostructures 12. In one embodiment, the n-type semiconductor layer18 can include an Al_(x)Ga_(1-x)N semiconductor layer having n-typedoping that functions as an n-type contact layer.

As noted above, each of the titled semiconductor heterostructures 12 caninclude regions having materials with different compositions. Inparticular, the core region 28 and the pair of shell regions 30 of thetilted semiconductor heterostructures can include materials withdifferent compositions. Having the core region 28 and the pair of shellregions 30 with materials of different compositions leads to therealization of the 2DG layers 20A, 20B having carrier densities at least10¹¹ carriers per square centimeters at each heterointerface 22, andthus, the formation of the 2DCA layers.

The core region 28 and the pair of shell regions 30 can include any ofthe aforementioned group III-V materials. In one embodiment, the groupIII-V material for the core region 28 and the pair of shell regions 30can include a group III nitride material. For example, the group IIInitride material can be represented by the Al_(x)Ga_(1-x)N system. Inone embodiment, the pair of shell regions 30 can have a differentcomposition of AlN than the composition of AlN in the core region 28.For example, the core region 28 can contain a higher molar fraction ofAlN than the pair of shell regions 30. For example, the molar fractionof AlN can be at least five percent higher for the core region 28 ascompared to the shell region(s) 30.

It is understood that other group III-V materials can be used for thecore region 28 and the shell regions 30. Furthermore, it is understoodthat combinations of these other group III-V materials for the coreregion 28 and the shell regions 30 can be used to attain the 2DG layers20A, 20B at the heterointerfaces 22, and thus the formation of the 2DCAlayers. Accordingly, the example of using the Al_(x)Ga_(1-x)N system torepresent the core region 28 and the shell regions 30 is not meant tolimit the scope of the various embodiments described herein. Other groupIII nitride material systems are equally applicable as are any systemsrepresenting group III-V materials.

FIG. 1 shows that the tilted features of the semiconductorheterostructures 12 include having the tilted surface of the sidewallsof the core region 28, the pair of shell regions 30 and the pair of 2DCAlayers formed at the heterointerfaces 22 slope increasingly inward froma surface of the light generating structure 16 of the semiconductorstructure 14 to a surface of the supply electrode 24. These tiltedfeatures allow the 2DG layers 20A, 20B, and thus the 2DCA layers, tocontact both a surface of the light generating structure 16 and thesupply electrode 24. This eliminates highly resistive regions thatnormally occur in horizontally laid out heterostructures. By notincorporating layers with high vertical resistance, the opto-electronicdevice 10 can have improved p-type conductivity, and as a result,increased efficiency and reliability. It is understood that these tiltedfeatures are illustrative of only one configuration and that the tiltedsemiconductor heterostructures of this embodiment as well as othersdescribed herein can include other representations of surfaces thatslant or tilt. Furthermore, these tilted can be effectuated by etchingor any other available methods.

In operation, a source applied to the supply electrode 24 can driveelectrons from the n-type semiconductor layer 18 to the light generatingstructure 16 and holes in the 2DCA layers at the heterointerfaces 22 ofthe tilted semiconductor heterostructures 12 to the light generatingstructure 16 for electron-hole pair recombination and light emissiontherefrom. In this embodiment, because holes are injected from the setof the tilted semiconductor structures 12, the 2DCA layers formed at the2DG layers 20A, 20B of the heterointerfaces of different compositions ofmaterial, act as two-dimensional hole accumulation (2DHA) andtwo-dimensional hole gas (2DHG) layers. It is understood that, while notshown for clarity, the device 10 will further include an electrode tothe n-type layer 18.

Injection of the electrons from the n-type semiconductor layer 18 andholes from the 2DHA and 2DHG layers in this embodiment and otherdescribed herein leads to improved carrier injection. In particular,improved carrier injection can be due to high mobility of the 2DHG.

FIG. 2 shows a more detailed cross-sectional view of one of the tiltedsemiconductor heterostructures 12 depicted in FIG. 1 along with aqualitative band diagram 32 showing the formation of one of the 2DGlayers 20 at the heterointerface 22 between the two materials withdifferent compositions according to an embodiment. In particular, thequalitative band diagram 32 of FIG. 2 plots electron potential energyversus distance along the heterointerface 22 where the 2DG layer 20 isformed, between one sidewall of the core region 28 and one of the shellregions 30.

The qualitative band diagram 32 is representative of an embodiment inwhich the core region 28 and the shell regions 30 are formed of groupIII nitride materials that include AlGaN. In this embodiment, the coreregion 28 includes a high concentration of Al, while the shell regions30 include a low concentration of Al. The qualitative band diagram 32 ofFIG. 2 corresponds to a 20% Al composition difference between the coreregion 28 and the shell regions 30. As shown in FIG. 2, the qualitativeband diagram exhibits a spike in the electron potential energy at apoint 34 on the heterointerface 22 that corresponds to a distance of 20nm from the core center. This spike is indicative of a hole accumulationlayer that results from an interface of semiconductor layers withdifferent polarization. Note that the qualitative band diagram 32 doesnot take into account the tilted features of the core region 28, theshell regions 30, the heterointerface 22, and the 2DG layer 20, which asexplained herein, improves the carrier injection of an opto-electronicdevice that utilizes such tilted semiconductor heterostructures 12having heterointerfaces of material with different compositions.

FIG. 3 shows another detailed cross-sectional view of one of the tiltedsemiconductor heterostructures 12 with the angle θ formed between one ofthe 2DG layers 20 and a bottom surface 36 of the heterostructureaccording to an embodiment. As noted above, the core region 28 of thetilted heterostructure 12 can include a different composition of a groupIII-V material than that of the shell regions 30. In an embodiment inwhich the core region 28 and the shell regions include a group IIInitride material, the core region 28 can have a different composition ofone of the elements in this material than that element in the shellregions 30. For example, if the core region 28 and the shell regions 30include AlGaN, then the core region can have a higher concentration ofAl than the concentration of Al in the shell regions. Also, as discussedherein and further shown in FIG. 3, the sidewalls of the core region 28,the pair of shell regions 30 and the pair of 2DCA layers formed at theheterointerface 22 in the 2DG layers 20 each have a sloping surface.Each 2DCA layer at the heterointerface 22 forms the angle θ with thesurface 36 which is formed on the light generating structure 16 of thesemiconductor structure 14. The angle θ is depicted in FIG. 3 withrespect to the C-axis which is a crystal axis and is parallel to theepitaxial growth direction.

Generally, the polarization charges that occur at a heterointerfacebetween group III nitride layers will depend on several factors. Forexample, the polarization charges will typically depend on the layercomposition (e.g., Al, In and Ga), the strain between the layers at theheterointerface, as well as the layer orientation with respect to thegrowth direction. Conventional devices, such as for example, highelectron mobility transistors, are typically formed using layers withtheir surfaces perpendicular to the C-axis of the material because thisproduces the strongest polarization charges. As the angle between theperpendicular to the heterointerface plane and the C-axis increases, thepolarization changes. FIG. 4 illustrates the relationship between thepolarization of a surface and its dependence upon a polar angle θ. FIG.4 shows that as the angle θ increases from 0 degrees to approximately 60degrees, the absolute value of polarization will decrease fromapproximately 4×10¹² cm⁻² to nearly zero.

The inventors to the various embodiments described herein havedetermined that an opto-electronic device, such as a UV LED, willprovide efficient carrier (i.e., hole or electron) injection if theangle θ between the heterointerface plane of the tilted heterostructure12 and the C-axis of the material growth direction is within a certainrange. Using FIG. 4 as a guideline, and assuming that highly efficientcarrier injection occurs if the 2DG layer 20 decreases by no more than 3times as compared to the horizontally laid out heterostructures 12 (zeroangle between the C-direction and the perpendicular to the surface ofthe heterostructure), the tilting angle θ of the heterostructuredepicted in FIGS. 1 and 3 can range from 30 degrees to 60 degrees. In anarrower embodiment, the tilting angle θ of the heterostructure does notexceed approximately 45 degrees.

Referring back to the detailed view of the tilted heterostructure 12 ofFIG. 2, in this example as noted with regard to the applicableembodiment of FIG. 1, the heterostructure is part of a set that forms ahole supply layer of the opto-electronic device 10. As a result, the 2DGlayers 20 form 2DHG layers so that hole injection occurs in part at the“injection zones” formed by a direct contact between the 2DHG layers andthe light generating structure 16 of the semiconductor structure 14. Itis understood that while holes in 2DHG along the heterointerface 20 canbe injected through injection zones, some holes can be also injectedthrough the core region 28 and even through the shell region 30.

If the angle θ of the heterostructure were changed, then such a changewould lead to variations in the 2DHG density and the distances ofinjection zones between locations along the 2DHG and the lightgenerating structure 16 into which the holes are injected. For example,smaller values of the angle θ will lead to a higher 2DHG density at theheterointerface 22, but also result in larger distances between theinjection zones. Accordingly, those skilled in the art will appreciatethat the selection of the angle θ that is used for the embodimentsdescribed herein as well as any opto-electronic devices that incorporatethe features of the tilted semiconductor heterostructures 12 will dependon a multitude of factors. For example, the angle θ that is selected candepend on the shape and sizes (e.g., thickness) of the tiltedsemiconductor heterostructures 12, and the total size of the activeregion that forms the light generating structure 16. Other factors caninclude, but are not limited to, other properties of an opto-electronicdevice that are not directly related to p-type conductivity. Forexample, if the opto-electronic device comprises an LED or aphoto-detector, the angle θ can be chosen to improve light extractionefficiency (in case of an LED) or photon absorption (in case of aphoto-diode).

FIG. 5 shows a cross-sectional view of an opto-electronic device 38 thatis similar to the opto-electronic device 10 of FIG. 1. In addition tothe components identified with like reference numerals, theopto-electronic device 38 of FIG. 5 includes a doped semiconductor layer40 formed between the set of tilted semiconductor heterostructures 12and the supply electrode 24 according to an embodiment. The dopedsemiconductor layer 40, which can be a single layer or a multi-layeredstructure, can facilitate the electric contact between the supplyelectrode 24 and the 2DCA layers in each of the tilted semiconductorheterostructures 12 in order to reduce the total resistance of theopto-electronic device 38. As illustrated in FIG. 5, the dopedsemiconductor layer 40 can include discontinuous sections 42 of thedoped semiconductor layer. In one embodiment, each of the discontinuoussections 42 of the doped semiconductor layer 40 can be formed on one ofthe tilted semiconductor heterostructures 12. The spacing between thediscontinuous sections 42 can be filled with a dielectric, such asambient air.

The doped semiconductor layer 40 can include one of multitude ofmaterials. For example, the doped semiconductor layer 40 can include,but is not limited, to Al_(x)B_(y)In_(z)Ga_(1-x-y-z)N layer with 0≦x, y,z≦1 and 0≦1-x-y-z≦1. In general, the molar fractions x, y, and z arechosen to yield a material with high p-type conductivity. For example,in an embodiment the molar fractions can comprise x=y=z=0, resulting ina GaN semiconductor. In an alternative embodiment, the dopedsemiconductor layer can comprise a superlatticeAl_(x1)B_(y1)In_(z1)Ga_(1-x1-y1-z1)N/Al_(x2)B_(y2)In_(z2)Ga_(1-x2-y2-z2)Nof layers where the molar fractions x1, y1, z1, x2, y2, z2 are selectedto result in a structure having barriers and quantum wells within thesuperlattice.

In the embodiment of FIG. 5, because the tilted semiconductorheterostructure 12 acts as a hole layer as noted with regard to theapplicable embodiment of FIG. 1, the doped semiconductor layer 40 can bea p-type doped semiconductor layer. An additional p-type dopedsemiconductor layer inserted between the supply electrode 24 and thehole injection structure of the tilted semiconductor heterostructures12, can facilitate the electric contact between the supply electrode 24and the 2DHG layers, thus reducing the total resistance of the device38.

In one embodiment, an opto-electronic device can include a currentspreading semiconductor layer 43, which can be epitaxially grown betweenthe light generating structure 16 and the set of tilted semiconductorheterostructures 12. For example, a p-type current spreadingsemiconductor layer 43 can be epitaxially grown between the lightgenerating structure 16 and the set of tilted semiconductorheterostructures 12. In one embodiment, the thickness of the currentspreading layer, as well as the lateral and vertical conductivity of thelayer, and the spacing between the tilted semiconductor heterostructures12 can be used to attain a certain current density variation. Forexample, the thickness, the lateral conductivity, and the verticalconductivity of the current spreading layer 43, along with the largestspacing between the heterostructures 12, can be used to attain a p-typecurrent density variation in the set of tilted semiconductorheterostructures that is at most 200% between any two points at thecurrent spreading layer 43 and the light generating structure 16. Inanother embodiment, a p-type current spreading semiconductor layer canbe epitaxially grown between the light generating structure 16 and theset of tilted semiconductor heterostructures 12. In this embodiment, thelargest distance between the tilted semiconductor heterostructures 12can be selected to be no larger than the current spreading length in thep-type current spreading semiconductor layer.

FIG. 6 shows a cross-sectional view of an opto-electronic device 44 thatis also similar to the opto-electronic device 10 of FIG. 1. In additionto the components identified with like reference numerals, theopto-electronic device 44 of FIG. 6 differs from the device 10 of FIG.1, in that the predetermined spacing S between the set of tiltedsemiconductor heterostructures 12 is increased. This increased spacingbetween each of the tilted semiconductor heterostructures 12 can be usedin sensing applications in which gases and/or liquids are permitted totravel through these spaces and contact a surface of the lightgenerating structure 16 in the semiconductor structure 14. In essence,the spaces between the tilted semiconductor heterostructures 12 formsensing regions 46 in the opto-electronic device 44 that allow it toperform sensing functions. While not shown for clarity, it is understoodthat one or more surfaces of the opto-electronic device 44 can beencapsulated to protect the gases and/or liquids from contacting thesesurfaces.

The predetermined spacing S between the tilted semiconductorheterostructures 12 can vary depending on the intended sensingapplications for the opto-electronic device 44. In one embodiment, aspacing that ranges from a few tens of nanometers (e.g., approximately30 nm) to a few tens of microns (e.g., approximately 30 microns) isgenerally sufficient to permit gases and/or liquids to travel therethrough and contact the surface of the light generating structure 16. Itis understood that spacing selection is likely to be limited by theequipment needed for photolithography and etching, as such approachescan be used to produce the tilted semiconductor heterostructuresdescribed herein. In an alternative embodiment, the tilted semiconductorheterostructures can be epitaxially grown to produce tiltednano-structures having a shell-core structure described herein.

It is understood that the amount of spacing S between the tiltedsemiconductor heterostructures 12 can a have role in the operatingcharacteristics of the opto-electronic device. In particular, thespacing between the tilted semiconductor heterostructures 12 can alsohave a role in enabling the opto-electronic device 44 to achieve atargeted total output of optical power. For example, in a scenario wherethe tilted semiconductor heterostructures 12 are used to form anopto-electronic device having an array of UV LEDs, the device cangenerate a higher total output of optical power if the spacing S betweenthe heterostructures is smaller because more heterostructures can beconfigured in an array of the same lateral size.

FIG. 7 shows a cross-sectional view of an opto-electronic device 48 thatis similar to the opto-electronic device 10 of FIG. 1 and theopto-electronic device 38 of FIG. 5, except the opto-electronic device48 is a flipped version of the embodiments depicted in FIGS. 1 and 5. Inparticular, FIG. 7 shows a cross-sectional view of the opto-electronicdevice 48 having the set of tilted semiconductor heterostructures 12formed over the semiconductor structure 14 having the light generatingstructure 16 and a p-type semiconductor layer 50 in which eachheterostructure includes 2DG layers at the heterointerface 22 betweentwo materials with different compositions according to an embodiment.

In this embodiment, the set of tilted semiconductor heterostructures 12act as the electron supply layer while the p-type semiconductor layer 50underneath the light generating structure 16 acts as the hole supplylayer, and the supply electrode 24 forms the cathode of theopto-electronic device 48. The anode of the opto-electronic device 48 isnot shown for clarity. As a result, the 2DG layer 20 formed at theheterointerfaces 22 between the core region 28 and the shell regions 30becomes a 2DEG layer in each heterostructure 12. In this manner,electron injection occurs at the injection zones formed by the directcontact between the 2DEG layers and the light generating structure 16 ofthe semiconductor structure 14. For example, in operation, a sourceapplied to the supply electrode 24 can drive electrons from theheterostructures 12 into the light generating structure 16 along withthe holes from the p-type semiconductor layer 50 for electron-hole pairrecombination and light emission.

FIG. 8 shows a schematic of an opto-electronic device 52 according to anembodiment in which the set of tilted semiconductor heterostructures 12are formed in an array 54 of rows and columns. In one embodiment, thearray 54 of tilted semiconductor heterostructures 12 can take the formof an ultraviolet lamp. In this manner, each the tilted semiconductorheterostructures 12 can act as a LED each having the aforementioned 2DCAlayers with the 2DHG or 2DEG injection structure. This allows the array54 of semiconductor heterostructures 12, which each function as theindividual pixels.

Although not represented in the top view of FIG. 8, it is understoodthat beneath each of the tilted semiconductor heterostructures 12 wouldbe the other elements that enable the heterostructures to act as a LEDsuch as, but not limited to, the light generating structure 16 and theunderlying electron supply layer or hole supply layer. In oneembodiment, the array 54 of tilted semiconductor heterostructures 12 canoperate as lasers. In still another embodiment, the array 54 of tiltedsemiconductor heterostructures 12 can operate as a combination of LEDsand lasers. As illustrated, the tilted semiconductor heterostructurescan include a core region 28 that is at least partially or completelylaterally surrounded by the shell region 30.

FIG. 9 shows a cross-sectional view of an opto-electronic device 56having a set of tilted semiconductor heterostructures 12 in which eachheterostructure includes a core region 28 with a set of shell regions 30adjoining the sidewalls of the core region, wherein each shell regionincludes a plurality of compositional layers (30A, 30B, 30C) accordingto an embodiment. As shown in FIG. 9, the compositional layers (30A,30B, 30C) can be formed on the sidewall of the core region 28 and extendlaterally away from the core region. In one embodiment, eachcompositional layer (30A, 30B, 30C) can have a different compositionfrom an immediately adjacent compositional layer. For example, thecompositional layers 30A, 30B, and 30C, which can include any of theaforementioned group III-V materials can have different composition ofmaterial. In one embodiment, the compositional layers 30A, 30B, and 30Ccan differ by the composition of at least one of the elements in thegroup III-V material used for these layers. For example, thecompositional layers 30A, 30B, and 30C can each have a differentcomposition of Al. In one embodiment, the set of tilted semiconductorheterostructures can have compositional layers with different molarfractions of the group III-V material at the heterointerfaces of thelayers. For example, some of the compositional layers can have lowermolar fractions of AlN, while other compositional layers can have highermolar fractions of AlN at the heterointerfaces of the layers. In oneembodiment, the difference in composition or molar ratio of AlN betweenany of the adjacent compositional layers is at least 1%. The dopingconcentration of the compositional layers can be varied, and in someinstances, the doping is selected to be delta doping at least somedistance away from the heterointerface.

The difference in composition between the compositional layers 30A, 30B,and 30C causes a 2DG to be formed at the heterointerface between each ofthe layers, layers having different composition. In the embodimentdepicted in FIG. 9, the 2DG formed at the heterointerfaces between eachof the compositional layers 30A, 30B, and 30C is a 2DHG layer becausethe set of tilted semiconductor heterostructures 12 act as a hole supplylayer and the n-type semiconductor layer 18 underneath the lightgenerating structure 16 functions as the electron supply layer. Forexample, the compositional layer 30A can have a first composition andthe compositional layer 30B can have a second composition resulting inthe heterointerface between layers 30A and 30B having a 2DHG.

The use of multiple compositional layers at the shell region 30 thatadjoin the core region 28 and extend laterally away from the sidewall ofthe core region can be advantageous over other embodiments which onlydepict the exterior shell regions having a single layer. For example,multiple shells allow for several injection zones, thus increasing theinjection of holes into an active region.

It is understood for embodiments in which a p-type semiconductor layeris used underneath the light generating structure 16 in place of then-type semiconductor layer 18, and the set of tilted semiconductorheterostructures 12 act as an electron supply layer, the 2DG layersformed at the interfaces of the compositional layers 30A, 30B, and 30Cwould include 2DEG layers. Also, the number of compositional layers 30A,30B, and 30C is only illustrative of one design option and it isunderstood that the each of the tilted semiconductor heterostructures 12can have more or less compositional layers than that depicted in FIG. 9.

FIG. 10 shows a cross-sectional view of an opto-electronic device 58that is also similar to the opto-electronic device 56 of FIG. 9,although any combination of one or more of the unique features shown canbe implemented on any embodiment described herein. In addition to thecomponents identified with like reference numerals, the opto-electronicdevice 58 of FIG. 10 differs from the device 56 of FIG. 9, in that thecore region 28 of each tilted semiconductor heterostructure includes amultilayered structure 60 that is surrounded by the compositional layers(30A and 30B) of the shell region 30. As shown in FIG. 10, themultilayered structure 60 can include a structure of horizontallyextending layers. In one embodiment, the multilayered structure 60 caninclude a short period superlattice (SPSL) having a plurality ofbarriers alternating with a plurality of quantum wells. To this extent,the SPSL can be transparent to a targeted radiation at a normalincidence to the SPSL. In one embodiment, the barriers and quantum wellsof the SPSL can include alternating Al_(x)Ga_(1-x)N/Al_(y)Ga_(1-y)Npairs, with each layer within a pair including a thin semiconductorlayer having a thickness ranging from 0.5 nm to 20 nm. The compositionof x and y of the SPSL in this embodiment can be selected to result inrelative transparency of the SPSL to the target radiation with anacceptable conductivity of such a SPSL structure.

In the embodiment depicted in FIG. 10 in which the set of tiltedheterostructure semiconductors act as the hole supply layer, themultilayered structure 60 in the core region 28 can be p-type doped witha doping profile that is selected to optimize the conductivity of theSPSL. For example, the doping of the multilayered structure 60 can beselected such that the barriers layers within the SPSL are heavily dopedin the proximity of SPSL quantum wells. In particular, the barrierslayers within the SPSL are the layers with a wider bandgap, and thuswill have a higher molar fraction of the material used for the SPSLlayers (e.g., AlN). It is these barrier layers that can be heavilydoped, while the quantum well layers of the SPSL have the narrow bandgapand lower molar fraction of the material used (e.g., AlN). It isunderstood that the barriers and quantum wells of the SPSL can includealternating layers of other group III nitride material besides AlN, aswell as group III-V materials as discussed herein.

The use of a multilayered structure 60 in the core region 28 such as aSPSL structure and the shell region 30 that adjoin the core region 28and extend laterally away from the sidewall of the core region can beadvantageous over other embodiments which only include a core regionwithout a multi-layered structure. For example, a multilayered structurecan promote injection of holes from 2DHG into a core region. Inaddition, the multilayered structure can be doped to result in holeconductivity across such a structure. Furthermore, such a structure cancomprise partially transparent and partially reflective layer that canbe beneficial for the efficiency of the opto-electronic device.

FIG. 11 shows a cross-sectional view of an opto-electronic device 62that is also similar to the opto-electronic device 58 of FIG. 10,although any combination of one or more of the unique features shown canbe implemented on any embodiment described herein. In this embodiment,the opto-electronic device 62 includes a set of ohmic contacts 64 formedover the set of tilted semiconductor heterostructures 12 that provide anincreased surface for improved p-type metal-to-semiconductor contact. Asshown in FIG. 11, each ohmic contact 64 is formed on one of the tiltedsemiconductor heterostructures 12. In one embodiment, each ohmic contact64 extends along a top surface of the core region 28 and the set ofshell regions 30 including the compositional layers (30A and 30B) anddown a side portion of each shell region and the compositional layers.Although the ohmic contacts 64 are shown extending down a limitedportion of the sides of the shell regions 30 and the compositionallayers 30A and 30B, it is understood that the extent to which the ohmiccontacts 64 cover these sides is variable, and thus the implementationdepicted in FIG. 11 is only illustrative and not meant to limit thevarious embodiment described herein.

The ohmic contacts 64 can be formed from a material that is transparentand reflective to a target radiation. For example, the ohmic contacts 64can be formed from materials that include, but are not limited to, Ni,Rd, Pd, Pt, and/or Ru, followed by Al. The ohmic contacts 64 can also beformed from multiple layers of any of the above materials. In oneembodiment, the ohmic contacts 64 can be formed from several metalliclayers.

For example, the ohmic contacts 64 can include a first layer thatincludes a transparent nickel layer, a second layer that includes ametal diffusion protective layer, followed by a third layer thatincludes a reflective layer. U.S. patent application Ser. No.13/711,675, titled “Ultraviolet Reflective Contact,” and on filed Dec.12, 2012 provides more detail of such an ohmic contact that includesseveral metallic layers, and is hereby incorporated by reference.

The opto-electronic device 62 can further include a dielectric layer 66formed in the spaces between each of the tilted semiconductorheterostructures 12 for passivation of the device. In one embodiment,the dielectric layer 66 is formed in the spaces between each of thetilted semiconductor heterostructures 12 such that the dielectricadjoins the portions of the shell regions 30 and the compositionallayers 30A, 30B that are not covered by the ohmic contacts 64. As shownin FIG. 11, the dielectric layer 66 can be formed to adjoin against aportion of the ohmic contacts 64 that extend along the side portion ofthe shell regions 30 and the compositional layers 30A, 30B. To thisextent, a top portion of the ohmic contacts 64 is located above thedielectric layer 66.

The dielectric layer 66 can be formed from a material that istransparent to a target radiation at a normal incidence to thedielectric layer. For example, the dielectric layer 66 can be formedfrom materials that include, but are not limited to, SiO₂, AAO, CaF₂,MgF₂, sapphire AlN, and/or the like. In one embodiment, the dielectriclayer 66 can have a transparency that is at least 30% transparent to thetarget radiation at a normal incidence to the dielectric layer.

As shown in FIG. 11, the opto-electronic device 62 can also include areflective metallic contact layer 68 that can reflect the targetradiation, and improve light extraction/light absorption efficiency ofthe opto-electronic device. The reflective metallic contact layer 68 cancover the top portions of the ohmic contacts 64 and the portions of thedielectric layer 66 that are formed between the tilted semiconductorheterostructures 12. The reflective metallic contact layer 68 can beformed from materials that include, but are not limited to, Al, Rd,and/or Pt. In one embodiment, the reflective metallic contact layer 68can include a multilayer metallic film. An example of a multilayermetallic film can include, but is not limited to, Rhodium, Palladium,and/or Aluminum alloys.

In another embodiment, a reflective mirror can be formed over the set oftilted semiconductor heterostructures 12 prior to the formation of thereflective metallic contact layer 68. In particular, the reflectivemirror can cover the top portions of the ohmic contacts 64 and theportions of the dielectric layer 66 that are formed between the tiltedsemiconductor heterostructures 12. The reflective metallic contact layer68 can then be formed over the reflective mirror. In this manner, thereflective mirror can improve the reflective properties of thereflective metallic contact layer 68. In one embodiment, the reflectivemirror can include a Bragg reflective mirror.

FIG. 12 shows a cross-sectional view of an opto-electronic device 70that is also similar to the opto-electronic device 62 of FIG. 11,although any combination of one or more of the unique features shown canbe implemented on any embodiment described herein. In this embodiment,the opto-electronic device 70 can include light scattering elements 72formed in the dielectric layer 66 to further improve light extractionefficiency from the device and reduce absorption of the light due tototal internal reflection. In general, the light scattering elements 72can scatter light that is at least 10% Lambertian. The light scatteringelements 72 can include, but are not limited to, voids, and amorphousdielectric materials such as SiO₂, CaF₂, MgF₂, sapphire, AAO and/or thelike. As shown in FIG. 12, the light scattering elements 72 can havedifferent shapes, sizes (e.g., thicknesses) and profiles.

The opto-electronic device 70 of FIG. 12 can further include a SPSL 74having a plurality of barriers alternating with a plurality of quantumwells and a semiconductor layer 76 formed between the set of tiltedsemiconductor heterostructures 12 and the light generating structure 16.As shown in FIG. 12, the SPSL 74 has a surface that directly contacts abottom surface of each of the tilted semiconductor heterostructures 12and a bottom surface of the dielectric layer 66. An opposing surface ofthe SPSL 74 directly contacts a surface of the semiconductor layer 76.The other surface of the semiconductor layer 76 is in immediate contactwith a surface of the light generating structure 16. In thisconfiguration, the SPSL 74 serves to spread the holes injected from holeinjection zones over the entire area of the active region. In addition,such a structure can partially reflect target radiation from the activeregion and help light extraction from the device. The semiconductorlayer 76 can serve to reduce the mechanical stresses exerted on activelayer. In addition, the semiconductor layer 76 can contain an electronblocking layer, as well as a layer for further spreading anddistributing holes over a lateral area of the active layer.

The SPSL 74 and its set of barriers alternating with the set of quantumwells can include, but is not limited to, group III-V materials. Thecomposition of the SPSL 74 including the barriers and wells can includea constant composition or a graded composition. In one embodiment, theSPSL 74 including the barriers and wells can include, a SPSL comprisingAl_(x)Ga_(1-x)N/Al_(y)Ga_(1-y)N layer with molar fraction x beingdifferent from molar fraction y.

The semiconductor layer 76 can include, but is not limited to,B_(W)Al_(X)Ga_(Y)In_(Z)N, where 0≦W, X, Y, Z≦1, and W+X+Y+Z=1. In oneembodiment, the semiconductor layer 76 can include any of theaforementioned group III-V materials. For example, the semiconductorlayer 76 can include, an Al_(x)Ga_(1-x)N semiconductor layer. Thesemiconductor layer 76 can have a graded composition or a constantcomposition. It is understood that the function of the semiconductorlayer 76 is subject to the doping of the various other layers in theopto-electronic device 70. For example, in embodiments in which thetilted semiconductor heterostructure are of a p-type, then thesemiconductor layer 76 can act as an electron blocking layer adjacent tothe light generating structure 16.

FIG. 13 shows another detailed cross-sectional view of one of the tiltedsemiconductor heterostructures 12 in an opto-electronic device 78 inwhich the compositional layers 30A, 30B, 30C of the shell region 30 havea graded composition of material that varies in a vertical directionaccording to an embodiment. A graded composition as used herein means acomposition with the molar ratio varying continuously as a function ofcoordinate z, wherein coordinate z is directed normal to thesemiconductor layer lateral area. As noted above, each of thecompositional layers (30A, 30B, 30C) can have a different composition ordifferent molar fraction of material (e.g., group III-V material) froman immediately adjacent compositional layer. The difference incomposition between the compositional layers 30A, 30B, and 30C causes a2DG to be formed at the heterointerface between each of the layershaving different composition. A 2DG gas is also formed at theheterointerface between the compositional layer 30C and the core region28 due to the difference in composition.

In FIG. 13, the composition of the compositional layers 30A, 30B, 30Care represented by Q2, B2, Q1, respectively, while the compositional ofthe core region 28 is represented by B1. At least one of thecompositions Q2, B2, Q1, B1 can have a graded composition that varies ina vertical direction as denoted by the directional arrow in FIG. 13. Inone embodiment, the compositions Q2 and Q1 can have a higherconcentration of material in comparison to the compositions of thematerial in B2 and B1. For example, in a scenario where thecompositional layers 30A, 30B, 30C and the core region 28 include agroup III nitride material, such as AlN, the compositions Q2 and Q1 canhave a higher concentration of the AlN in comparison to the compositionsof the AlN in B2 and B1. It is understood that other group III-Vmaterials can be used for the compositional layers 30A, 30B, 30C and thecore region 28, and the example of AlN is not meant to limit the scopeof the various embodiments described herein.

The vertically graded composition of the compositional layers 30A, 30B,30C and the core region 28 not only contributes to the formation of the2DG layers at the heterointerfaces between the materials of differentcomposition, but the grading of the composition of these layers canresult in a polarization doping of the tilted semiconductorheterostructure 12 as it is known in art. For example, in the scenariowhere the set of tilted heterostructures 12 act as a hole supply layer,the graded composition of the various regions in a heterostructure willresult in a p-type polarization doping. Alternatively, if the set oftilted heterostructures 12 act as an electron supply layer, the gradedcomposition of the various regions in a heterostructure would result inan n-type polarization doping.

The grading of composition of the compositional layers and the coreregion of a tilted semiconductor heterostructure are not limited tograding in a vertical direction. In one embodiment, the compositionallayers of the shell region and the core region of a tilted semiconductorheterostructure can include having at least one of the layers with acomposition that is graded in a lateral direction. FIG. 14 shows adetailed cross-sectional view of one of the tilted semiconductorheterostructures 12 in which the compositional layers of the shellregion have a graded composition of material that varies in a lateraldirection according to an embodiment. A tilted semiconductorheterostructure 12 with any of the regions having a grading that extendsin a lateral direction will modify the bandgap structure of theheterostructure 12. In particular, the graded composition can result ina hole accumulation layer that is spread through a volume domain due topolarization doping. Such volume accumulation layers are known in art.

The effect that a layer with a graded composition in a lateral directionwill have on the bandgap structure of a heterostructure is illustratedin FIGS. 15A-15B. In particular, FIGS. 15A-15B show the effect that aheterostructure with and without a laterally graded composition. Thelateral grading of group III nitride semiconductor material results inthe spreading of a 2DHG layer as represented by the carrier densityprofiles in the figures according to an embodiment. More specifically,FIG. 15A shows the bandgap structure for a composition layer having acomposition of a material Q1 that is graded, while FIG. 15B shows thebandgap structure for a layer Q1 having no grading. As can be seen fromFIG. 15A, the grading of Q1 results in spread of accumulated holesthroughout the volume of Q1 layer, while without grading, the holes aremore localized over a portion of a Q1 layer as shown in FIG. 15B.

As shown in FIGS. 15A-15B, the grading of a layer in a region of thetilted semiconductor heterostructure 12 results in a wider carrierdensity profile (D2 in FIG. 15A), while an ungraded layer results in anarrower carrier density profile (D1 in FIG. 15B). As a result, thoseskilled in the art will appreciate that the grading of a region within atilted semiconductor heterostructure 12 can be used control thespreading of the 2DG at the heterointerfaces with other layers. Note,that the exact grading control of the layers with the materials Q1 andQ2, respectively, depends on the growth process of such semiconductorlayers, and in general, can result in a grading that is not exactly asshown in FIGS. 13-14, but can comprise a grading that extends in bothvertical and lateral directions.

In addition to affecting the electrical properties of the tiltedsemiconductor heterostructures 12, the shape, size and composition ofthe core region 28 and the shell region 30 including any compositionallayers can have a role in the optical properties that are attained withthe tilted semiconductor heterostructures 12. For example, the opticalproperties of the tilted semiconductor heterostructures 12 can becontrolled by correctly selecting the composition and thicknesses of thelayers that form each of the heterostructures.

In one embodiment, the compositional layers of the shell region can bedesigned to form a Bragg reflector structure that can partially reflectthe light and increase the light extraction efficiency of the device.FIG. 16 shows a detailed cross-sectional view of one of the tiltedsemiconductor heterostructures 12 in an opto-electronic device 80 inwhich the compositional layers 30A, 30B, 30C, 30D of the shell region 30form a Bragg reflector structure 82 through selecting the thickness andcomposition of each layer. In particular, each layer can have athickness of approximately one quarter of a target wavelength, bepartially transparent to target radiation, and have refractive indexchange between the layers 30A, 30B, 30C and 30D.

In another embodiment, the compositional layers of the shell region canbe designed to form a graded refractive index structure for improvedlight extraction from such regions. In particular, the compositionallayers 30A, 30B, 30C, 30D can form the graded refractive index structurein the shell region 30 by selecting a molar ratio for each layer to havean appropriate index of refraction. For example, the layer 30A can havean index of refraction N_(a), layer 30B an index of refraction N_(b),layer 30C an index of refraction N_(c), and layer 30D an index ofrefraction N_(d), such that N_(d)>N_(c)>N_(b)>N_(a). In one embodiment,a shell 30 can comprise a single graded layer with a molar fractionchanging in a lateral direction to result in graded index of refractionN_(g), such that N_(g) is smallest at the ambient/material interface andlargest at the shell/core interface.

For either embodiment in which the tilted semiconductor heterostructures12 include the Bragg reflector structure 82 or the graded refractiveindex structure, the core region 28 of each heterostructure can betransparent to a targeted radiation at a normal incidence to the coreregion. In one embodiment, the core region 28 of the heterostructure 12can have a transparency that is at least 30% transparent for the lightpropagated normal to the base of the heterostructure throughout theheight of the structure.

FIG. 17 shows a detailed cross-sectional view of one of the tiltedsemiconductor heterostructures 12 in an opto-electronic device 84 inwhich the core region 28 includes a plurality of core regions 28A, 28B,28C adjoined by shell regions 30 having a plurality of compositionallayers 30A, 30B, 30C, 30D according to an embodiment. Having a coreregion 28 with a multiple of core regions 28A, 28B, 28C in conjunctionwith shell regions 30 having a multiple of compositional layers 30A,30B, 30C, 30D adjoining the core regions can be useful in optimizingboth light extraction characteristics of the opto-electronic device 84,as well as the conductivity of the set of tilted semiconductorheterostructures 12. In particular, each core region can serve itspurpose for the efficient operation of the device. For instance, onecore region (28C) can comprise a semiconductor spreading layer used toevenly spread holes throughout the active layer. In some instances, thecore region 28C can comprise a region designed to reduce mechanicalstresses on the active region. In an embodiment, the core region 28C cancomprise a compositionally graded region (wherein the grading is in thelayer normal direction), resulting in polarization doping. In anembodiment, such a region can further comprise a sub-region being anelectron blocking layer, where the electron blocking layer has a widerband gap than the active region layer. The core region 28B can comprisea partially transparent/conductive region for promoting holeconductivity through the core. Such a region can comprise anAl_(y1)Ga_(1-y1)N/Al_(y2)Ga_(1-y2)N superlattice. In addition, such aregion can promote light extraction by having superlattice layersselected to result in partial reflection of target radiation. The coreregion 28A can comprise a heavily p-type doped semiconductor layerdesigned to form and adequate ohmic contact with a metallic contactlayer.

In one embodiment, optimization can be attained by optimizing the wallplug efficiency of the opto-electronic device 84 including the set oftilted semiconductor heterostructures 12 which entails selecting thelateral, vertical size of the tilted semiconductor structures, as wellas selecting the tilt inclination (e.g., the shape of the semiconductorstructures 12). Additional parameters can include the thickness,composition, and number of shell layers. The optimal parameters foroptimizing the wall plug efficiency can be determined through iterationsof parameters using numerical modeling. For optimization, it isfrequently important to optimize the wall plug efficiency of a devicecontaining conical structures, and optimal parameters can be foundthrough iterations of parameters using numerical modeling.

The multiple of core regions 28A, 28B, 28C and compositional layers 30A,30B, 30C, 30D in the heterostructure 12 of FIG. 17 can include differentcompositions of any of the aforementioned materials. For example, themultiple of core regions 28A, 28B, 28C and compositional layers 30A,30B, 30C, 30D in the heterostructure 12 can include a group III-Vmaterial. In one embodiment, the multiple of core regions 28A, 28B, 28Cand compositional layers 30A, 30B, 30C, 30D can include AlGaN such thateach layer is represented by the Al_(x)Ga_(1-x)N system. For example, asshown in FIG. 17, the compositional layers 30A, 30B, 30C, 30D can berepresented by Al_(x1)Ga_(1-x2)N, Al_(x2)Ga_(1-x2)N, Al_(x3)Ga_(1-x3)N,Al_(x4)Ga_(1-x4)N, respectively, while the core regions 28A, 28B, 28Ccan be represented by Al_(xN)Ga_(1-xN)N,Al_(y1)Ga_(1-y1)N/Al_(y2)Ga_(1-y2)N, Al_(x5)Ga_(1-x5)N, respectively. Inan embodiment, x_(N) can be chosen to be 0, and y1 and y2 can rangebetween 0.1 and 0.9. In an embodiment, the molar fraction x5 can dependon the growth coordinate z and vary between 1 and 0.

FIG. 18 shows a cross-sectional view of an opto-electronic device 86having a plurality of tilted semiconductor heterostructures 88 formedfrom a plurality of nanowires 90 in which each nanowire includes 2DGlayers at a heterointerface between two materials with differentcompositions according to an embodiment. In FIG. 18, the plurality oftilted semiconductor heterostructures 88 can be formed over thesemiconductor structure 14 having a light generating structure 16 and ann-type semiconductor layer 18, in which each heterostructure 12 includes2DG layers at the heterointerface 22 between two materials withdifferent compositions according to an embodiment. In addition, the setof tilted semiconductor heterostructures 88 can be formed between thelight generating structure 16 and the supply electrode 24, while then-type semiconductor layer 18 of the semiconductor structure 14 can beformed on the substrate/buffer 26.

Each tilted semiconductor heterostructure 88 formed from a nanowire 90can include a core region 28, a set of shell regions 30, with each shellregion adjoining a sidewall of the core region. The sidewalls of thecore region 28, and the pair of shell regions 30 at the heterointerface22 each have a sloping surface.

The light generating structure 16 can form the active region of theopto-electronic device 86. In one embodiment, the light generatingstructure 16 can include a multi-quantum well structure having a set ofbarrier layers alternating with a set of well layers. In the embodimentdepicted in FIG. 18, the n-type semiconductor layer 18 can form anelectron supply layer, while the set of tilted semiconductorheterostructures 88 formed from nanowires can form a hole supply layer.In this manner, the light generating structure 16, the n-typesemiconductor layer 18, and the set of tilted semiconductorheterostructures 88 form a heterostructure within the opto-electronicdevice 86 that serves as the active p-n junction region forelectron-hole pair recombination and light emission. The supplyelectrode 24, which can be a metal electrode, acts as the anode side ofthe opto-electronic device 86. A source (not shown) applied to thesupply electrode 24 can drive electrons from the n-type semiconductorlayer 18 to the light generating structure 16 and holes in the 2DGlayers at the heterointerfaces 22 of the tilted semiconductorheterostructures 12 to the light generating structure 16 forelectron-hole pair recombination and light emission therefrom.

Each of the titled semiconductor heterostructures 88 formed from thenanowires 90 can include regions have materials with differentcompositions. In particular, the core region 28 and the pair of shellregions 30 of the tilted semiconductor heterostructures can includematerials with different compositions. Having the core region 28 and thepair of shell regions 30 with materials different compositions leads tothe realization of the 2DG layers.

The core region 28 and the pair of shell regions 30 can include any ofthe aforementioned group III-V materials. As mentioned above, the groupIII-V material for the core region 28 and the pair of shell regions 30can include a group III nitride material. For example, the group IIInitride material can represented by the Al_(x)Ga_(1-x)N system. In oneembodiment, the pair of shell regions 30 can have a differentcomposition of Al than the composition of Al in the core region 28. Forexample, the core region 28 can contain a higher concentration ormolarity of Al and the pair of shell regions 30 can have a lowerconcentration or molarity of Al. In one embodiment, the first AlN molarratio in the core region 28 can be greater than the second AIN molarratio in the shell regions 30.

The tilted features of the semiconductor heterostructures 88 formed fromthe nanowires 90 include having the tilted surface of the sidewalls ofthe core region 28 and the pair of shell regions 30 formed at theheterointerfaces 22 slope increasingly inward from a surface of thelight generating structure 16 to a surface of the supply electrode 24.These tilted features allows the 2DG layers to contact a surface of thelight generating structure 16 and the supply electrode 24. As describedabove with respect to FIG. 1, the nanowires can form an angle θ with asurface of the light generating structure 16. In one embodiment, theangle θ can range from 30 degrees to 60 degrees. It is understood thatthe nanowires 90 can be grown under the angle θ with respect to thelight generating structure 16.

In operation, a source applied to the supply electrode 24 can driveelectrons from the n-type semiconductor layer 18 to the light generatingstructure 16 and holes in the 2DG layers at the heterointerfaces 22 ofthe tilted semiconductor heterostructures 88 to the light generatingstructure 16 for electron-hole pair recombination and light emissiontherefrom. In this embodiment, because holes are injected from the setof the tilted semiconductor structures 88, the 2DG layers formed at theheterointerfaces of different compositions of material, act as 2DHGlayers.

It is understood that the implementation depicted in FIG. 18 is onlyrepresentative of one possibility and is not meant to limit the scope ofthe various embodiments. For example, the n-type semiconductor layer 18can be replaced by a p-type semiconductor layer. In this manner, the setof tilted semiconductor heterostructures 88 formed of nanowires 90 canact as an electron supply layer and the heterointerfaces formed at thedifferent compositions of material act as 2DEG layers. The holes andelectrons recombine in the light generating structure for electron-holepair recombination and light emission.

In one embodiment, the invention provides a method of designing and/orfabricating a circuit that includes one or more of the opto-electronicdevices with tilted semiconductor heterostructures designed andfabricated as described herein. To this extent, FIG. 19 shows anillustrative flow diagram for fabricating a circuit 1260 according to anembodiment. Initially, a user can utilize a device design system 1100 togenerate a device design 1120 for a semiconductor device as describedherein. The device design 1120 can comprise program code, which can beused by a device fabrication system 1140 to generate a set of physicaldevices 1160 according to the features defined by the device design1120. Similarly, the device design 1120 can be provided to a circuitdesign system 1200 (e.g., as an available component for use incircuits), which a user can utilize to generate a circuit design 1220(e.g., by connecting one or more inputs and outputs to various devicesincluded in a circuit). The circuit design 1220 can comprise programcode that includes a device designed as described herein. In any event,the circuit design 1220 and/or one or more physical devices 1160 can beprovided to a circuit fabrication system 1240, which can generate aphysical circuit 1260 according to the circuit design 1220. The physicalcircuit 1260 can include one or more devices 1160 designed as describedherein.

In another embodiment, the invention provides a device design system1100 for designing and/or a device fabrication system 1140 forfabricating a semiconductor device 1160 as described herein. In thiscase, the system 1100, 1140 can comprise a general purpose computingdevice, which is programmed to implement a method of designing and/orfabricating the semiconductor device 1160 as described herein.Similarly, an embodiment of the invention provides a circuit designsystem 1200 for designing and/or a circuit fabrication system 1240 forfabricating a circuit 1260 that includes at least one device 1160designed and/or fabricated as described herein. In this case, the system1200, 1240 can comprise a general purpose computing device, which isprogrammed to implement a method of designing and/or fabricating thecircuit 1260 including at least one semiconductor device 1160 asdescribed herein. In either case, the corresponding fabrication system1140, 1240, can include a robotic arm and/or electromagnet, which can beutilized as part of the fabrication process as described herein.

In still another embodiment, the invention provides a computer programfixed in at least one computer-readable medium, which when executed,enables a computer system to implement a method of designing and/orfabricating a semiconductor device as described herein. For example, thecomputer program can enable the device design system 1100 to generatethe device design 1120 as described herein. To this extent, thecomputer-readable medium includes program code, which implements some orall of a process described herein when executed by the computer system.It is understood that the term “computer-readable medium” comprises oneor more of any type of tangible medium of expression, now known or laterdeveloped, from which a stored copy of the program code can beperceived, reproduced, or otherwise communicated by a computing device.

In another embodiment, the invention provides a method of providing acopy of program code, which implements some or all of a processdescribed herein when executed by a computer system. In this case, acomputer system can process a copy of the program code to generate andtransmit, for reception at a second, distinct location, a set of datasignals that has one or more of its characteristics set and/or changedin such a manner as to encode a copy of the program code in the set ofdata signals. Similarly, an embodiment of the invention provides amethod of acquiring a copy of program code that implements some or allof a process described herein, which includes a computer systemreceiving the set of data signals described herein, and translating theset of data signals into a copy of the computer program fixed in atleast one computer-readable medium. In either case, the set of datasignals can be transmitted/received using any type of communicationslink.

In still another embodiment, the invention provides a method ofgenerating a device design system 1100 for designing and/or a devicefabrication system 1140 for fabricating a semiconductor device asdescribed herein. In this case, a computer system can be obtained (e.g.,created, maintained, made available, etc.) and one or more componentsfor performing a process described herein can be obtained (e.g.,created, purchased, used, modified, etc.) and deployed to the computersystem. To this extent, the deployment can comprise one or more of: (1)installing program code on a computing device; (2) adding one or morecomputing and/or I/O devices to the computer system; (3) incorporatingand/or modifying the computer system to enable it to perform a processdescribed herein; and/or the like.

The foregoing description of various aspects of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formdisclosed, and obviously, many modifications and variations arepossible. Such modifications and variations that may be apparent to anindividual in the art are included within the scope of the invention asdefined by the accompanying claims.

What is claimed is:
 1. A device, comprising: a semiconductor structurehaving a semiconductor layer including one of an n-type semiconductorlayer and a p-type semiconductor layer, and a light generating structureformed on the semiconductor layer; and a plurality of tiltedsemiconductor heterostructures formed over the semiconductor structure,each tilted semiconductor heterostructure separated from an adjacenttilted semiconductor heterostructure by a predetermined spacing, eachtilted semiconductor heterostructure including a core region, a set ofshell regions, each shell region adjoining a sidewall of the coreregion, and a set of two-dimensional carrier accumulation (2DCA) layers,each 2DCA layer formed at a heterointerface between one of the sidewallsof the core region and one of the shell regions, the sidewalls of thecore region, the set of shell regions and the set of 2DCA layers eachhaving a sloping surface, wherein each 2DCA layer forms an angle with asurface of the semiconductor structure, the angle ranging from 30degrees to 60 degrees.
 2. The device of claim 1, wherein the core regionand the set of shell regions of each of the tilted semiconductorheterostructure includes a combination of different materials, whereinthe combination of different materials forms a two-dimensional gas (2DG)in each of the 2DCA layers at an interface between the combination ofdifferent materials.
 3. The device of claim 2, wherein the 2DG compriseone of a two-dimensional hole gas (2DHG) and a two-dimensional electrongas (2DEG).
 4. The device of claim 3, further comprising a supplyelectrode formed over the plurality of tilted semiconductorheterostructures.
 5. The device of claim 4, wherein the set of 2DCAlayers in each of the plurality of tilted semiconductor heterostructurescontacts the semiconductor structure and the supply electrode.
 6. Thedevice of claim 4, further comprising a doped semiconductor layer formedbetween the plurality of tilted semiconductor heterostructures and thesupply electrode, wherein the doped semiconductor layer comprisesdiscontinuous sections of the doped semiconductor layer, eachdiscontinuous section of the doped semiconductor layer formed on one ofthe plurality of tilted semiconductor heterostructures.
 7. The device ofclaim 4, wherein the tilted surface of the sidewalls of the core region,the set of shell regions and the pair of 2DCA layers slopes increasinglyinward from the surface of the semiconductor structure to a surface ofthe supply electrode.
 8. The device of claim 1, wherein each of theplurality of tilted semiconductor heterostructures comprise a tiltednanowire.
 9. The device of claim 1, wherein the set of shell regions ofat least one tilted semiconductor heterostructure comprise a pluralityof compositional layers formed on the sidewall of the core region thatextend laterally away from the core region, each compositional layerhaving a different composition from an immediately adjacentcompositional layer, wherein a two-dimensional gas (2DG) is formedbetween each of the compositional layers.
 10. The device of claim 9,wherein the core region of the at least one tilted semiconductorheterostructure comprises a multilayered structure of horizontallyextending layers, wherein the multilayered structure comprises a shortperiod superlattice (SPSL) having a plurality of barriers alternatingwith a plurality of quantum wells, wherein the first SPSL is transparentto a targeted radiation at a normal incidence to the first SPSL.
 11. Thedevice of claim 10, wherein each of the layers in the plurality ofcompositional layers and the multilayered structure comprises a groupIII-V material, wherein the group III-V material comprises a materialrepresented by the Al_(x)Ga_(1-x)N system, and each of the layersincludes a different composition of Al.
 12. The device of claim 10,further comprising a plurality of ohmic contacts formed over theplurality of tilted semiconductor heterostructures, wherein each ohmiccontact is formed on one of the tilted semiconductor heterostructures,the ohmic contact extending along a top surface of both the core regionand the set of shell regions and down a side portion of each shellregion.
 13. The device of claim 12, further comprising a dielectriclayer formed in the spaces between each of the plurality of tiltedsemiconductor heterostructures, wherein the dielectric layer istransparent to a targeted radiation at a normal incidence to thedielectric layer.
 14. The device of claim 13, further comprising lightscattering elements formed in the dielectric layer, wherein the lightscattering elements scatter light that is at least 10% Lambertian. 15.The device of claim 9, wherein each of the compositional layerscomprises a graded composition of material, wherein the gradedcomposition of material varies in one of a vertical direction, a lateraldirection, or a combination of both the vertical direction and thelateral direction.
 16. A device, comprising: a substrate; an n-typesemiconductor layer formed over the substrate; a light generatingstructure formed on the n-type semiconductor layer; a plurality ofspaced conically-shaped p-type heterostructures formed over the lightgenerating structure, each conically-shaped p-type heterostructureincluding a core region and a set of shell regions each adjoining asidewall of the core region, wherein a two-dimensional hole gas (2DHG)layer is formed at a heterointerface between each of the sidewalls ofthe core region and the shell regions, the sidewalls of the core region,the set of shell regions, and the 2DHG layers each having a tiltedsurface that slopes increasingly inward from a bottom surface of thecore region, the pair of shell regions, and the 2DHGs to a top surfacethereof, wherein the heterointerface forms an angle with a surface ofthe light generating structure, the angle ranging from 30 degrees to 60degrees; and a supply electrode formed over the plurality ofconically-shaped p-type heterostructures.
 17. The device of claim 16,wherein the n-type semiconductor layer, the light generating structure,and the plurality of spaced conically-shaped p-type heterostructures areeach formed of a group III-V material.
 18. The device of claim 17,wherein the core region and the set of shell regions of each of theplurality of spaced conically-shaped p-type heterostructures have adifferent composition of AlN, the core region containing a higherconcentration of AlN than a concentration of AlN in the set of shellregions, wherein each of the set of shell regions of each tiltedsemiconductor heterostructure comprises a plurality of compositionallayers formed on the sidewall of the core region that extend laterallyaway from the core region, each compositional layer having a differentcomposition of AlN from an immediately adjacent compositional layer,wherein a difference in composition of AlN between any of the adjacentcompositional layers is at least 1%.
 19. The device of claim 18, whereina two-dimensional gas (2DG) layer is formed between each of thecompositional layers, wherein the 2DG layer is at least 10¹¹ carriersper square centimeters.
 20. An opto-electronic device, comprising: anultraviolet transparent substrate; an n-type semiconductor layer formedover the ultraviolet transparent substrate, the n-type semiconductorlayer having an Al_(x)Ga_(1-x)N composition; a light generatingstructure formed on the n-type semiconductor layer, the light generatingstructure including a plurality of barriers alternating with a pluralityof quantum wells, the plurality of barriers and the plurality of quantumwells having an Al_(x)Ga_(1-x)N and Al_(y)Ga_(1-y)N composition,respectively, with x<y; a p-type semiconductor structure formed over thelight generating structure, the p-type semiconductor structure includingat least one layer including a set of tilted semiconductorheterostructures, each tilted semiconductor heterostructure separatedfrom an adjacent tilted semiconductor heterostructure by a predeterminedspacing and having a lateral area that is no larger than 20% of alateral area of the light generating structure, each tiltedsemiconductor heterostructure having an Al_(x)Ga_(1-x)N composition,each tilted semiconductor heterostructure including a core region and aset of shell regions, each shell region adjoining a sidewall of the coreregion, wherein the core region includes a first AlN molar ratio andeach of the shell regions surrounding the core region include a secondAlN molar ratio, the first AlN molar ratio being greater than the secondAlN molar ratio.